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Investigation of Static and Transient Characterisitcs of 4H-SiC IGBT using High-K DielectricsAuthor: vidya.naidu Date: 2017-07-27 Report no: IIIT/TH/2017/58 Advisor:Sivaprasad Kotamraju,Srivatsava Jandhyala AbstractSiliconCarbide(SiC) is a wide band gap semiconductor with high thermal conductivity, high electron saturation velocity and high critical electric field properties. Silicon based devices, if replaced by SiC devices, could reduce the switching losses and improve the power conversion efficiency in grids becauseof their high frequency capability. However, the main limitation of SiC based MOS devices is thei r inability in handling higher electric fields at the oxide interface. An alternative to overcome this limitation is to replace the conventionally used SiO 2 with the high-K dielectrics that can sustain high electric fields. High-K dielectrics ZrO 2 and HfO 2 , with a dielectric constant of about 25, have been chosen for this study, as SiO 2 , with a dielectric constant of 3.9, cannot sustain high electric fields. This approach has been attempted earlier with HfO 2 as the gate dielectric in the case of SiC power MOSFETs. Previous studies of SiC MOSFETs with HfO 2 /SiO 2 stacking gate dielectric have shown significant improvement in the electronic performance. The electric field in the high-K dielectrics does not exceed the safe operational value, even when the underneath SiC has exceeds high electric field values. In order to address these concerns, an asymmetric trench gate SiC IGBT using high-K dielectrics such as HfO 2 and ZrO 2 as alternatives to the conventionally used SiO 2 has been studied. While supporting high electric field is one aspect, in this work it is investigated whether replacement of SiO 2 with the high-K dielectrics considered has any influence on the switching characteristics of IGBTs such as rise time, fall time, and turn OFF time using TCAD (Technology Computer-Aided Design) simulations. The static and switching characteristics of the SiC IGBT have been explored using technology based two-dimensional numerical computer simulations. ZrO 2 and HfO 2 exhibited better forward transcon-ductance ratio and reduced tail current thereby indicating improved power losses. The power dissipation curves were found to be consistent with the results obtained. However, these high-K dielectrics have low band offset as compared to SiO 2 -SiC interface. A lower band offset could lead to a high gate leakage current, which was resolved by introducing a thin layer of SiO 2 between SiC and high-K dielectrics. Power dissipation has been analyzed for IGBT with SiO 2 , HfO 2 and ZrO 2 layers by applying a pulse signal. In addition, the power dissipation is simulated for temperature range of 300-600K for different dielectric layers as the switching performance of a device is supposed to deteriorate with increase in temperature. HfO 2 and ZrO 2 demonstrated good temperature stability. The work in this paper is an attempt to correlate the power dissipation with the static and dynamic characteristics for the respective oxide layers. Full thesis: pdf Centre for VLSI and Embeded Systems Technology |
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